Mechanical performance and microstructure of HSLWC incorporating MWCNTs and shale-based aggregates

High-strength lightweight concrete (HSLWC) made with shale ceramsite (SC) and shale pottery sand (SPC) is a sustainable way to reduce the use of natural resources and lower the environmental impact of regular concrete. As a result, interest in HSLWC has been growing. Nanomaterials are of interest because they can improve mechanical properties. In this study, SC and SPC were used as the coarse and fine aggregates to explore how multi-walled carbon nanotubes (MWCNTs) affect the mechanical properties and microstructure of HSLWC. The tests measured slump, density, compressive strength, and splitting tensile strength. The mix design followed the M40-grade high-strength concrete standard. MWCNTs was added at 0.00%, 0.05%, 0.10%, and 0.15% of the cement weight. The results showed that small amounts of MWCNTs made the concrete more compact. They also lowered the slump and improved the mechanical properties. After 28 days, the compressive strength of HSLWC with MWCNTs was between 44.2 MPa and 55.4 MPa. The highest splitting tensile strength was 4.2 MPa at 0.10% MWCNTs. The dry density was between 1542 kg/m³ and 1589 kg/m³. This meets the standard for high-strength lightweight aggregate concrete. Scanning electron microscopy (SEM) showed that MWCNTs connected cracks in the cement and mixed with hydration products. This stopped microcracks from growing. As a result, the concrete had better fracture strength and toughness. This is a useful way to make HSLWC stronger.